Another way that works sometimes is this, it might take quite a few times to make it work but it should eventually. Go to settings>application manager>select all apps by scrolling all the way to the right>scroll down to Google Services Framework>then clear data and force stop>back out and go to system update>and select update firmware and Samsung software it should say last update was in 1969. I did this on my nexus 7 for the 4.2 update and it worked after a few tries. Hope this works, if not the qbking77 video is really easy to do also, all you need is a microsd card.
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